Codecs may use non-binary short media defect (SMD) detection algorithms. The principle SMD detection is to detect consecutive sign-disagreements between an extrinsic output of a detector and decoder indicative of a media defect (e.g. a storage media defect).
An underlying assumption for such algorithms to work well is that the probability of two-bit sign disagreement (2SD) is higher than the probability of one-bit sign disagreement (1SD), and the probability of 1SD is higher than the probability of 0-bit sign disagreement (0SD) in the defect locations.